Micromegas detectors are known comprising a gas enclosure that is filled with a suitable gaseous mixture, such a detector enabling the amplification of electrons by an avalanche process.
As illustrated in FIG. 1, a first category of micromegas detector 1 relates to conventional micromegas detectors comprising notably a cathode 2, an amplification micro-gate 3 and an anode 4 provided with reading tracks 5 connected to a reading device 6. The cathode 2, the amplification micro-gate 3 and the anode are arranged in a gas enclosure 7. The cathode 2 diverts the electrons to the reading tracks 5, whereas the amplification micro-gate 3 makes it possible to amplify the signal so that it is read. In order to amplify the signal passing through the amplification micro-gate 3, an electric voltage of approximately 500 V is applied to the amplification micro-gate 3.
During the implementation of such a micromegas detector 1, the electric voltage is increased progressively on the amplification micro-gate 3 until 500 V are obtained. Above this value of 500 V, sparks appear between the amplification micro-gate 3 and the reading tracks 5 making the micromegas detector 1 momentarily inoperative. Normally, the sparks develop where impurities are situated, in other words between the reading tracks 5 and the amplification micro-gate 3. Then, the plasma of the spark vaporises the impurity and the voltage may continue to be increased up to the value of 500 V.
Moreover, sparks may also be produced when the micromegas detector 1 is operational. These sparks generally appear when the flux of particles becomes too intense. The micromegas detector 1 then undergoes breakdowns making the voltage drop and discharging the amplification micro-gate 3. During the time taken to re-establish the electric voltage of the amplification micro-gate 3, around 1 ms, the micromegas detector 1 is inoperative.
The development of breakdowns in the micromegas detector 1 is often a limiting factor in extreme conditions of use, notably in very high particle fluxes generating therein drops in gain as well as a possible degradation of the micromegas detector 1 in the long term.
In order to reduce the amplitude and the impact of breakdowns, a second category of micromegas detector 20 has been developed, namely so-called resistive micromegas detectors. As illustrated in FIG. 2, this type of resistive micromegas detector 20, moreover comprises resistive tracks 21 connected to the common ground M21 and positioned facing reading tracks 5. The reading tracks 5 and the resistive tracks 21 are moreover separated by an insulating layer 22. The presence of these resistive tracks 21 makes it possible to avoid the formation of the breakdown, and to evacuate the charges to the common ground M21. Hence, resistive micromegas detectors 20 are particularly sensitive to impurities. In fact, not being able to break down, it is no longer possible to eliminate the impurities during the powering up of the amplification micro-gate 3. If an impurity is present or is introduced into the resistive micromegas detector 20, an important leakage current makes the whole of the resistive micromegas detector 20 difficult to use. Also, resistive micromegas detectors 20 have to be assembled in a clean room so as to reduce the risk of introducing dust. The use of a clean room for the assembly of resistive micromegas detectors 20 in order to leave the minimum of dust on the reading tracks 5 significantly increases the manufacturing costs without however guaranteeing 100% cleanliness reliability.
Moreover, despite assembly in a clean room, resistive micromegas detectors remain not very reliable for usage outside of the laboratory. In fact, it is possible that a dust of around 50 μm is introduced via the introduction of gas into the gas enclosure. To overcome this problem, numerous pressurised water washings are regularly carried out.